Warming Pacific 'primed' for possible El Nino forming by this spring

Farmers beware: a build-up of warm water in the tropical eastern Pacific has lifted the odds for an El Nino forming late this spring, the Bureau of Meteorology said.

Five of the eight models used by the bureau now point to El Nino thresholds being crossed, a shift in climate patterns that would typically produce lower-than-average rain across eastern Australia.

An El Nino can point to a dry spell for eastern Australia - which would be bad news for dairy farmers such as Brendan Hayden, from Pilton, Queensland, who are already being forced to provide fodder for their herds. Credit:Peter Rickards

"The ocean is primed for an El Nino but it will need a push from the atmosphere" to get there, Robyn Duell, a senior climatologist at the bureau, said. "It will depend a lot on what happens to the trade winds in the next couple of weeks."

At present, the odds for an El Nino are about 50-50 but even a near miss can still translate into lower-than-average rain and hotter temperatures for much of the country. Given the winter outlook is already pointing to the continuation of the drier-than-usual conditions, those areas already in drought might be in for an extended dry spell.

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Australia posted its fourth-warmest autumn by maximum temperatures on record, while NSW had its hottest and Victoria, its second-warmest. Rainfall was a third-below average for the season, while May alone was the third-driest in national records going back to 1910.

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During El Nino years, easterly equatorial trade winds slow or reverse. The Pacific Ocean also absorbs less heat from the atmosphere, adding a temperature kick to the background warming from climate change.

The impacts of El Ninos on Australia are typically worst when reinforced by a so-called positive Indian Ocean Dipole, when temperatures off north-western Australia are relatively cool compared with those off eastern Africa. So far, only one of the models used by the bureau point to a positive-IOD forming, Ms Duell said.

Globally, May was the fourth warmest on record, with the other three coming since 2014, according to international agencies such as NASA.

The previous three months - marking the northern spring - were the third warmest in 138 years of records.